After six decades of launches, the launch of the very last Delta rocket on Tuesday (April 9) marked a change in the way the US sends satellites, interplanetary probes and spacecraft into orbit.
United Launch Alliance (ULA) has ignited its final Delta IV Heavy rocket to launch NROL-70, a classified payload for the U.S. National Reconnaissance Office (NRO). The powerful booster took off from Space Launch Complex-37 (SLC-37) at the Cape Canaveral Space Force Station in Florida at 12:53 a.m. EDT (1653 GMT) and literally set itself on fire for the 16th and final time.
“It’s a bittersweet moment for us,” Tory Bruno, CEO of United Launch Alliance, said in a call with reporters on March 26. “It’s such an amazing piece of technology – 23 stories high, a million gallon hall of propellant, two and a quarter million pounds of thrust and the most metallic of all rockets, which ignites itself before it goes into space. “
That spectacle, unique to the Delta IV in its heaviest configuration, was the result of hydrogen building up in the flame trench and then rising alongside the rocket after being used to cool the three RS-68A engines to cryogenic temperatures. When the engines started, the hydrogen ignited and the flames hit the orange insulation covering the core stage and the two side-mounted boosters.
“That’s why we had nice toasted marshmallow boosters and the very dramatic effect of a self-immolating rocket before she went up,” Bruno said.
The two boosters were jettisoned about four minutes into the flight, followed by the core, or first stage, which separated a minute and 45 seconds later. A single RL10C-2-1 engine on Delta’s cryogenic second stage then took over, propelling the NROL-70’s payload into space. Due to national security concerns, news coverage of the launch stopped after the fairing jettisoned approximately 6 minutes and 40 seconds into the flight.
Related: Facts about ULA’s Delta IV Heavy rocket
ULA is retiring the Delta IV and eventually its other older rocket, the Atlas V, in favor of the newly introduced Vulcan, which performed a near-perfect first mission in January. The Vulcan was developed to replace both long-flying missiles in all their configurations.
“This is a great mission to think about that transition because national security space missions are at our core and the unique set of missions there requires a high-energy launch vehicle. We designed Vulcan specifically for that,” said Bruno.
Go Delta
Tuesday’s launch was not only the 16th Delta IV Heavy, but also the 45th Delta IV launch, the 35th Delta IV to fly from Florida and the 389th Delta launch of any kind since 1960 (294 of which were from Cape Canaveral were sent to heaven). ).
Half of the Delta IV Heavy launches were intended to deliver NRO payloads into orbit. The rocket and its lower-powered configurations were also used in support of NASA, NOAA (the U.S. National Oceanic and Atmospheric Administration), the U.S. Air Force, and commercial payloads.
The first Delta launch on May 13, 1960 attempted to launch the world’s first passive communications satellite experiment into space, but failed because the Delta’s thrusters failed to fire. (The Delta initially flew as a second stage atop a Thor ballistic missile, which is why the vehicle was called the Thor-Delta.)
Related: Meet the United Launch Alliance’s Delta Rocket family
Three months later, the Thor-Delta placed Echo IA into orbit, leading to the first successful satellite transmission and the first two-way communication between two points on Earth through space. That success was followed by the launch of the second weather satellite and Telstar-1, which made possible the first live transatlantic television feed.
Next came Delta B, a derivative of Thor-Delta, whose flights included the July 1963 launch of Syncom-2, the first satellite in geosynchronous orbit.
Introduced four months after the launch of Syncom-2, Delta C primarily carried NASA research satellites into orbit. The Delta D, which added three solid rocket engines to the Delta C configuration, deployed the first geostationary communications satellite in 1964 and the first commercial communications satellite, Intelsat I, a year later.
Related: A History of Rockets
Delta E launched a series of NASA Pioneer probes that measured interplanetary phenomena from widely separated points in space. Delta G (F was not built), a Delta E without a third stage, began launching a series of NASA satellites carrying biological specimens for research. Delta J was launched only once, K was not built and L introduced an elongated version of the Thor first stage.
Delta M and Delta N retired the alphabetical designations while being used to send more communications satellites to orbit.
The numerical series that followed included Delta 900, which sent NASA’s first LandSat meteorological satellite into space in 1972; Delta 2310, which launched the first Spanish satellite into orbit to study the ionosphere; and Delta 2914, which launched the first NOAA Geostationary Operational Environmental Satellite (GOES).
Delta 3000 introduced the payload assist module (PAM) to reach higher orbits. A 3000 series rocket was NASA’s first launch after the 1986 space shuttle Challenger tragedy, but it too was ill-fated and was destroyed before it could deploy the GOES satellite it carried.
Only three 4000 and one 5000 series rockets were launched, but they led the way to the Delta II, which flew in Lite and Heavy configurations.
The Delta II entered service in 1989 with the launch of the first operational Global Positioning System (GPS) satellite. In total, the Delta II has taken off 155 times over the course of almost 30 years, of which all but two flights were successful. A third of the launches were for NASA payloads, including sending eight robotic landers and rovers to Mars; a pair of twin probes to the moon; the first mission to orbit the planet Mercury; the first mission to orbit and land on an asteroid; and the first spacecraft to return a sample of a comet.
The Delta II also deployed the Spitzer Space Telescope and the Kepler Planet Hunting Observatory before launching for the final time in 2018 with NASA’s ICESat-2 Earth-observing satellite.
Delta III flew only three times. Two launches failed and the last had a dummy payload.
The Delta IV was developed for the U.S. Air Force’s Evolved Expendable Launch Vehicle (EELV) program. Originally flown by Boeing before the aerospace company partnered with Lockheed Martin to create ULA, the Delta IV and Delta IV Heavy became the primary rocket supporting U.S. military payloads.
The Delta IV Heavy was also used to launch NASA’s Orion spacecraft on its first unmanned Exploration Flight Test (EFT-1) in 2014 and sent the Parker Solar Probe on its way to “touch” the sun in 2018.
Delta on display
Through each of its versions and configurations, the Delta rocket family advanced and became more capable. To lift heavier payloads and send them further into space, the venerable launch vehicle gained larger tanks, added solid-mount rocket boosters, adopted improved engines and used more powerful upper stages.
The Delta IV Heavy, which was launched on Tuesday to conclude the program, was 72 meters high, more than 2.5 times the height of the original Thor Delta. At takeoff, the Delta IV Heavy generated 2.1 million pounds (9,341 kiloNewtons) of thrust, a significant increase from 150,000 pounds (667 kiloNewtons) in 1960.
“It just has a storied legacy and it’s done great things for our nation. We’re very proud to have been a part of that,” Bruno said. “And even though Vulcan is the future, I personally think it’s a shame to see it go away.”
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Despite its long history, today only a few Delta rockets are preserved in museums and rocket parks.
The Kennedy Space Center Visitor Complex in Florida displays a Thor Delta and Delta II in its Rocket Garden. Another Thor-Delta is on display at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The static firing unit for what became the Delta IV common booster core was delivered to the Air Force Space and Missile Museum (now the Cape Canaveral Space Force Museum) in 2007 and placed on outdoor display.
“We don’t have an extra Delta IV Heavy to put in a museum,” Bruno said. “So [this last rocket] definitely had a special feeling.”
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